Project description

Discfit reads disc permeameter data in the field and calculates hydraulic parameters of the soil; saturated hydraulic conductivity and Gardner’s alpha constant.

Disc permeameter is a tool for measuring hydraulic properties in the field. Steady-state periods in multiple constant head period are selected automatically from the data, and infiltration rate for each steady-state period is calculated. After that, infiltration rate at saturated condition is estimated by Gardner’s exponential model,

K(h) = Ks exp(αh)

where K is unsaturated hydraulic conductivity (cm/s), h is matric head (cm), Ks is saturated hydraulic conductivity (cm/s), α is a constant (/cm). Note that h is negative and αh is negative. Based on this equation, the linear relationship ln(q) = ln(qs) + αh is used for estimating qs (cm/s), the infiltration rate at the saturated condition, and α constant, as we have multiple point of (h, q) data from the disc permeameter. The hydraulic conductivity is calculated from the infiltration rate based on steady-state analysis of Wooding (1968);

q = K(1 + 4 / παr)

where α is the Gardner’s α and r is the diameter of the disc (cm). See equations (10) and (13) in Minastry and George (1999).